Daikai Subway Station Research Articles

Cyclic seismic pushover testing of a multi-story underground station

The experimental approach is crucial for investigating the seismic performance and damage process of underground structures. Considering the shortcomings of the 1-g, centrifuge shaking table and monotonic displacement pushover tests, a large-scale cyclic displacement pushover test method is proposed based on the soil-underground structure dynamic interaction and seismic performance quantification system. Taking a two-story three-span subway station structure as the prototype, the cyclic displacement pushover test device was designed for a 1/7-scale multi-story subway station based on the seismic response characteristics of underground structures. The corresponding numerical simulations and experiments were conducted. Typical numerical results (including the seismic damage process, capacity curves of the structural columns, and strain response) and test results (the macroscopic phenomenon of structural damage development, strain response, and deformation response) are interpreted. The results show that the proposed cyclic displacement pushover test is better than the monotonic displacement pushover test, the damage process of the tested station structure conforms to the description of the inter-story drift ratio (IDR) quantification system of seismic performance. Meanwhile, the column has greater strain amplitudes than other components, and the column strain curves reach their peaks before other components. Furthermore, the tested station structure has a similar damage pattern to the Daikai subway station. The reliability and feasibility of the proposed cyclic displacement pushover test method are verified.

Assessing Ground Motion Intensity Measures and Structural Damage Measures in Underground Structures: A Finite Element Analysis of the Daikai Subway Station

Research on the characterization of ground motion intensity and damage of underground structures is limited, while reasonable selection of ground motion intensity measures and structural damage measures is a crucial prerequisite for structural seismic performance evaluation. In this study, a two-dimensional finite element model of soil and structures was established based on the Daikai subway station in Japan. Through incremental dynamic analysis, 32 ground motion intensity measures and seven structural damage measures were comprehensively evaluated from seven properties, including efficiency, practicality, proficiency, scaling robustness, relativity, hazard computability, and sufficiency. According to the analysis results, the purpose and significance of each property during measure optimization were hierarchically sorted out. The results show that peak ground acceleration, acceleration spectrum intensity, and sustained maximum acceleration are recommended as ground motion intensity measures, while maximum inter-story drift ratio, column end displacement angle, and two-parameter measures are recommended as the structural damage measures for seismic performance evaluation of the shallow-buried subway station. Furthermore, measure optimization approaches are proposed as follows: the basic selection of IMs should satisfy scaling robustness, hazard computability, and sufficiency to site condition; the optimal selection of IMs is suggested to be evaluated mainly through efficiency, practicality and proficiency, and verified through relativity and relative sufficiency between IMs. The optimal selection of DM is suggested to be evaluated through four properties, including efficiency, practicality, proficiency, and relativity.

Fuzzy seismic fragility analysis of underground structures considering multiple failure criteria

To avoid the deficiency of a single failure criterion and deterministic thresholds of limit states in seismic fragility analysis of underground structures, a method of fuzzy seismic fragility analysis of underground structures considering multiple failure criteria is proposed by combining fuzzy-random theory and copula theory. In this method, probabilistic seismic demand and capacity analyses based on different failure criteria are first performed. Then, the fuzziness of the limit states of different failure criteria is characterized by using membership functions, and the fuzzy seismic fragility of underground structures considering a single failure criterion with different membership functions is further calculated. On this basis, the copula function and the combination of membership functions are optimized to characterize the correlation between multiple failure criteria and establish fuzzy seismic fragility curves considering multiple failure criteria. Taking the Daikai subway station as the background, the effects of different failure criteria and the fuzziness of limit states on the seismic fragility are discussed, and the optimal combination of membership functions that characterizes the fuzziness of limit states under the failure criteria of deformation and strength is also presented. The results show that the failure criteria and fuzziness of limit states have significant effects on the seismic fragility of underground structures, and the combination of trigonometric membership functions is the optimal combination that characterizes the fuzziness of multiple failure criteria. Moreover, the fuzzy seismic fragility of underground structures considering multiple failure criteria is more sensitive to the fuzziness of limit states under frequent earthquakes and basic earthquakes, while the multiple failure criteria and the correlation between different failure criteria have more significant effects on the fuzzy seismic fragility considering multiple failure criteria under rare earthquakes and extremely rare earthquakes.

Quasi-static model test and numerical simulation of a single-story double-span underground subway station

The model test method is crucial for studying the seismic performance of underground structures. Presently, model tests for the seismic response of underground structures are primarily performed with 1-g and N-g centrifuge shaking table. The 1-g shaking table model test is limited by the stress similarity in the soil-structure interaction system and cannot reproduce the seismic damage process and extent of the underground structure. The small table size of the N-g centrifuge model test makes it difficult to reflect the spatial effects of the seismic response of large underground structures. Seeking a large-scale model test method that can directly simulate the seismic damage process is essential for investigating the seismic performance of underground structures. Herein, based on the seismic response characteristics of underground structures, a quasi-static pushover test device applicable to underground structures was designed, and the corresponding tests and numerical model calculations were executed using the Daikai subway station as a prototype. Based on the macroscopic phenomena of structural damage development of the subway station in the test, the damage mechanism of the station structure was analyzed and compared with the numerical model. The strain amplitudes, displacements, and digital scatter strain color maps were analyzed to verify the reliability of the cyclic pushover loading test simulating the seismic performance level and damage process of the underground structure. Simultaneously, the rationality of the proposed quantification system for classifying the seismic performance level of single-story underground structures was verified.

Study on the effect of burial depth on seismic response and seismic intensity measure of underground structures

Considering the complexity of the soil-structure dynamic interaction mechanism, underground structures are restrained and influenced by the surrounding soil in earthquakes, and their seismic damage under strong earthquakes is different from that of above-ground structures. The seismic response of underground structures is influenced by several coupling factors, including structural form, ground motion parameters, and soil properties, etc. In addition, the burial depth of the underground structure is also one of the critical parameters affecting its seismic response. In this study, the computational model of soil-structure dynamic interaction at different burial depths was established by using the finite element software ABAQUS with a single-story, double-span Daikai subway station as the prototype. The influence laws of different burial depth conditions on the seismic response characteristics such as inter-story drift ratio, internal force of critical sections, and seismic damage of subway stations are systematically studied. Meanwhile, this paper compares the correlation and applicability of PGA (peak ground acceleration), PSSRD (peak site soil relative displacement), and SSSRD (structural side soil relative displacement) with the seismic response of underground structures under different burial depths by applying the principle of vulnerability analysis. The results show that PGA and SSSRD are relatively better IMs (intensity measure) in shallowly buried structures, while the relative superiority of PSSRD gradually increases with increasing burial depth, and PSSRD is a more reasonable IM in deeply buried underground structures.

Static pushover test of spring-underground structure system for seismic performance analysis of underground structure

The static test is appropriate for studying the seismic performance of underground structures due to the large size of the model structure and the controllable stress level. By setting elastic elements around the model structure, the static pushover test of the spring-underground structure system could simulate the initial stress state of the underground structure and soil-structure interactions during the pushover process. Taking the Daikai subway station damaged in the 1995 Hanshin earthquake in Japan as the model structure, a series of static pushover tests of underground structures with a geometric scale of 1/5 were performed. The impact of vertical ground motion on the seismic performance of underground structures was studied by conducting two static pushover tests of spring-underground structure system under different vertical loads; the impact of surrounding soil on the seismic performance and failure process of underground structures was studied by conducting static pushover tests with and without springs under the same vertical load. The relationship between the horizontal pushover force and the structural interstory drift, the concrete strain change process of structural weak vertical member, the structural failure phenomenon, and the seismic performance of the test object can be obtained from the tests, which can provide valuable information for experimental research on the seismic performance of underground structures. The test results demonstrate that the vertical ground motion decreases the ductility of underground structure, and the surrounding soil improves the lateral collapse resistance of underground structure.

Seismic performance and fragility analysis of underground subway station with rubber bearings

In this paper, a comparative study of the seismic response and fragility of a station structure before and after being retrofitted with an LNB installed on the top of its columns is conducted to evaluate the effectiveness of retrofitting measures in reducing risk probability employing, for the first time, a probabilistic approach. The Daikai subway station was adopted as a case study, and two-dimensional finite element models of soil-structure system with and without LNB were established. Incremental dynamic analyses (IDA) of original and retrofitted structures were conducted to evaluate their seismic responses under different ground motion intensities and considering the uncertainty of ground motion. Further, the IDA curve cluster and quantile lines of station structure and rubber bearing were constructed. Finally, the seismic fragility curves of structure and LNB were established for the risk assessment under different performance levels based on the structural performance index. The results demonstrated that the horizontal deformation, shear force and bending moment of the central column fitted with rubber bearings are greatly reduced compared with the actual Daikai station structure, which is more pronounced for lower ground motion intensity. In addition, the failure probability of the retrofitted structure corresponding to different damage levels is much lower than that of the original structure under the same ground motion intensity. Meanwhile, the probability of moderate to severe damage for the underground station structure is greatly reduced after retrofitting with the rubber bearings. The overall seismic performance of the structure is significantly improved and post-earthquake repair-demand is greatly decreased.

Stochastic ground motion simulation and seismic damage performance assessment of a 3-D subway station structure based on stochastic dynamic and probabilistic analysis

In practical engineering of underground structures, it is well-known that the randomness of earthquake generation and a structure's seismic response need to be considered for the safety of the project. The dynamic response and reliability level of a subway station are analyzed from the perspective of random vibration and the effect of stochastic ground motions on seismic responses is considered in this paper. This research proposes a model that can generate completely nonstationary ground motions and combines it with the probability density evolution method (PDEM) to analyze the seismic response and reliability level of a subway station. First, combining random function spectrum representation and evolutionary power spectrum density function, a probability model of nonstationary ground motion is established. According to the code (Gb 50909-2014), the model parameters of 5 sites are suggested, and the efficiency and accuracy are verified. A series of intensity–frequency nonstationary stochastic earthquakes are generated for the seismic response analysis. Then, a 3-D finite element analysis is performed for the deterministic dynamic response of the Daikai subway station, and the second-order statistics of three evaluation indicators (interstory drift, relative settlement, damage area ratio) are attained. Finally, the stochastic dynamic response and reliability level of the station structure are obtained by processing the data with the PDEM. The limit state related to the three evaluation indicators is established through probability density function (PDF) and cumulative distribution function (CDF). In addition, this probability evaluation system is more intuitive and effective than conventional methods. The statistical and probabilistic results show that the characteristics of earthquakes have a significant influence on the seismic response of subway stations, furthermore, the stochastic earthquakes generated by the intensity–frequency nonstationary ground motion model match well with the target value and the PDEM can comprehensively evaluate the seismic performance and reliability level of subway stations. Therefore, combing the stochastic earthquake and PDEM is an effective way to analyze the seismic response of subway stations.

Influence of soil to structure stiffness on the accuracy of the pushover method for underground structures

The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process. The method has been widely used in seismic design and other related scientific research; however, the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood. In this study, we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS. All models are computed by the dynamic time-history method or the pushover method. Furthermore, the dynamic time-history solution result is taken as the standard solution, and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section. The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method, and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1. The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.

Study on seismic failure mechanism of shallow buried underground frame structures based on dynamic centrifuge tests

During the Kobe earthquake in 1995, Daikai subway station suffered the severe collapse, which aroused people's more attention to the earthquake damage response of underground structures. In order to investigate the seismic failure mechanism of underground frame structures, a series of 1/50-scaled dynamic centrifuge tests were conducted. To make the underground structures produce a reasonable seismic failure mode in tests, an experimental scheme was designed in detail based on the author's previous numerical studies. With the purpose of simulating the vertical inertial effect of the overburden soil in the dynamic centrifuge tests, a certain proportion of steel grits were mixed into the overlying soil. A model structure finally occurred the overall collapse mode, which was similar to that of Daikai subway station. Based dynamic centrifuge tests, the seismic failure mechanism of shallow buried underground frame structure was analyzed and summarized in the paper. It could offer a reference for the cause of collapse of Daikai subway station. The series of tests provided valuable experimental data for further studies of the earthquake damage response of underground frame structures, and also enriched the testing technique for destructive model tests.

Stochastic Dynamic Response Analysis and Probability Evaluation of Subway Station Considering Subjected to Stochastic Earthquake Excitation

As a relatively new means of transportation, the subway has become an important tool for the sustainable development of many cities. Being buried deep in soil under the weight of vital infrastructure, subway stations can be vulnerable to seismic excitations. Considering the high randomness of ground motions, it is important to research the failure probability and seismic performance of the subway station based on stochastic dynamic analysis. In this paper, a probability density evolution method (PDEM) coupled with a spectral representation random function is used to analyze the stochastic dynamic response and seismic probability of a subway station. First, according to the improved power spectral density model and the seismic design code of urban rail transit structures in China (GB 50909-2014), a set of nonstationary ground motions consistent with the code spectrum are obtained. Then, a great deal of deterministic dynamic calculations for Daikai subway station considering soil–structure interaction based on elastic–plastic methods are performed. In addition, the nonlinear stochastic response analysis and the dynamic probability analysis are obtained for the subway station by solving the PDEM equation. Finally, the probability density function (PDF) and cumulative distribution function (CDF) of the subway station under stochastic earthquake excitations are obtained based on three performance indices, including drift angle in the middle column, relative vertical displacement between floor and roof, and damage area ratio (DAR). The results show that the stochastic dynamic analysis and the probability density evolution method can analyze seismic response and evaluate seismic performance of subway stations effectively. The proposed method will serve as an effective tool for the seismic design of underground structures.

A BOUNDARY FORCED RESPONSE DISPLACEMENT METHOD FOR SEISMIC ANALYSIS OF SYMMETRICAL UNDERGROUND STRUCTURES

A boundary forced response displacement method is proposed for the seismic analysis of symmetrical underground structures based on the requirement of quasi-static pushover test of soil-underground structure systems. The implementation procedure and special features of the method are introduced in detail. We took the Daikai subway station which was damaged during the Kobe earthquake in Japan as an example for the analysis, and compared the results of boundary forced response displacement method, the FEM seismic deformation method and the dynamic time-history analysis method. The results show that the accuracy of the new method was much higher than the FEM seismic deformation method when the width of the model was reasonable. The errors of the internal forces and the story drift were less than 15%. The new method is an effective simplified method for seismic response analysis of symmetrical underground structures. The attenuation law of lateral boundary forced displacement was analyzed. It provides references for the quasi-static pushover test of soil-underground structure system.

Research on earthquake damage mechanism of a subway station structure based on centrifuge shaking table tests and numerical analysis

During the 1995 Kobe earthquake, the Daikai subway station witnessed serious collapse, which attracted the attention of people to the earthquake damage response of the subway structure. To study the earthquake failure mechanism of a subway station structure, two comparative dynamic centrifuge tests were performed. During the centrifuge tests, many important physical quantities cannot be directly monitored with appropriate instruments due to many limitations, such as extremely small model structures, extremely high collection frequency and complex centrifugal environment. To study the earthquake failure mechanism of a subway station structure in depth, an extended analysis of model tests was performed by means of numerical model. Finally, the earthquake failure mechanism was summarized in detail based on the numerical analysis.

Seismic response and failure mechanism of underground frame structures based on dynamic centrifuge tests

AbstractDuring the 1995 Kobe earthquake in Japan, the Daikai subway station suffered total collapse, which made the research on the seismic failure mechanism of underground frame structures become a hot topic. The author has carried out a lot of research on earthquake failure mechanism of underground frame structures based on numerical method. To validate and further study the seismic failure response and mechanism of underground frame structures, a series of comparative dynamic centrifuge tests were carried out. The research conclusions are as follows. The vertical earthquake action significantly increased the axial pressure on the columns of an underground frame structure, reducing their horizontal deformation capacity. The columns subjected to high axial compression were prone to brittle damage under a relatively strong horizontal earthquake, which led to the overall collapse of an underground frame structure. The areas near the intersection of the ceiling slab and the sidewalls were the weak part of the underground frame structure and were vulnerable to tensile cracks under earthquake. The columns' top and bottom were the fragile parts and were prone to concrete cracking or even shear failure under an earthquake. If the columns could remain intact and effectively provided vertical support under a strong earthquake, it was beneficial to reduce the risk of the overall collapse of an underground frame structure.

Virtual hybrid simulation method for underground structures subjected to seismic loadings

Current knowledge on seismic analysis of underground structures is limited to analytical solutions, numerical methods and scaled model tests. Virtual hybrid simulation (VHS) is an efficient and economical analysis method that combines numerical approaches and experiment methods while taking the advantages of both. In this study, a VHS method employing a multi-axial experimental setup for seismic analysis of soil-structure systems is proposed and the corresponding VHS framework was developed using OpenFresco and OpenSees. To demonstrate the ability of the VHS method in accurately and efficiently capturing seismic behavior of underground structures, the proposed VHS method was applied to evaluate seismic response of the Daikai subway station, during which a good agreement was achieved when comparing the VHS results with those of the complete numerical simulation (CNS). Moreover, the advantages of the expanded multi-axial experimental setup in the proposed VHS method over the simplified single-DOF experimental setup are evaluated and discussed.

Structural dynamic response of underground structure with vertical ground motion input

Since many cases of structural damage in past earthquakes have been attributed to strong vertical ground motion, our understanding of vertical seismic load effects and their influence on seismic performance of subway station structure is limited. In this study, the Daikai subway station is taken as a typical example. A two-dimensional finite element model of both soil and structure was established using finite element software ABAQUS. Two input approaches of ground motion are considered, including the horizontal component alone and the vertical and horizontal motions simultaneously. Four groups of ground motion records are selected according to the site type of this station and scaled to the strong intensity which can make the station damage. Results show that the vertical seismic load increases the axial force of the column component apparently, while horizontal seismic load has little effect on axial compression ratio.

Upgrading the seismic performance of underground structures by introducing lead-filled steel tube dampers

Central-column failure can cause large underground structures to collapse during strong earthquakes. The use of lead-filled steel-tube dampers (LFSTDs) in the seismic design of such structures is proposed to mitigate or prevent such an eventuality. Three-dimensional nonlinear dynamic analyses of the Daikai subway station with and without LFSTDs under the action of the Hyogoken–Nambu earthquake has been performed, considering soil-structure interaction. The feasibility of the proposed method was verified from four aspects—force, deformation, damage, and energy dissipation. The effects of variability in seismic inputs, strength ratio, and arrangement mode of dampers on the structural dynamic response characteristics have been discussed. Results reveal that the application of LFSTDs to large underground structures remarkably reduces the force, deformation, and damage associated with the central column under seismic loading. Additionally, a strength ratio of 0.4 is recommended when using LFSTDs, whereas in cases without LFTSTDs, the strength of the central column must be appropriately enhanced.

Hybrid Simulation of Seismic Responses of a Typical Station with a Reinforced Concrete Column

During the 1995 Kobe earthquake, damages were observed in the Daikai subway station and adjacent tunnels. It was the first large-scale underground structure that failed under the earthquake excitation. Numerical and experimental analyses have been conducted to study the failure process of the Daikai station. However, the issue of the scale ratio still exists in the shaking table tests of underground structures. In order to tackle this issue, a hybrid simulation technique is developed here to study the seismic performance of a typical subway station. Based on the previous research, it is found that the central column is the critical component of the structure. Therefore, a reinforced concrete central column is physically tested in the hybrid simulation process. On the other hand, the remaining parts of the structure and soil domain are numerically modeled at the same time. Four hybrid simulation cases are conducted with peak ground accelerations of 0.01 g, 0.1 g, 0.22 g, and 0.58 g. The test results of displacement and shear force are compared with the analytical results. Moreover, the good agreement between the test results and numerical results validate the accuracy of the proposed hybrid test method. After the hybrid simulation process, a quasi-static test is conducted to illustrate the mechanical properties of the central column after the earthquake excitation.

Seismic fragility assessment of the Daikai subway station in layered soil

A numerical method based on nonlinear incremental dynamic analysis is proposed in this paper to develop seismic fragility curves for rectangular subway station buried in layered soil and subjected to transverse seismic excitations. The proposed method primarily consists of four parts, namely, model verification, damage quantification, ground motion processing, and seismic performance assessment. The main section of the Daikai subway station collapsed during the Kobe Earthquake is used as an example to demonstrate the detailed procedure of the proposed method in construction of seismic fragility curves for underground structures. Results from the nonlinear soil-structure interaction model in this paper is firstly verified against the results from existing literature. The threshold values of different damage states of the underground structure are quantified by interstory drift ratio obtained from the nonlinear static pushover analysis of the soil-structure interaction system. Based on the results of the incremental dynamic analysis, it is found that the peak acceleration at the ground surface is an efficient and appropriate intensity measure of the ground motions for shallowly buried underground structure. The proposed method is validated by comparing with the existing empirical and numerical seismic fragility curves of buried rectangular underground structures and can be used as an effective approach in the development of seismic fragility database for underground structures.

On collapse of Daikai subway station due to the 1995 Kobe earthquake - numerical simulation in case of thrusting up at lower grand layer -

On collapse of Daikai subway station due to the 1995 Kobe earthquake - numerical simulation in case of thrusting up at lower grand layer -